Addition Property of Equality

Property You can add the same number to both sides of an equation and the statement will still be true. If $a = b$, then $a + c = b + c$.

Examples To solve $x 5 = 12$, add 5 to both sides: $x 5 + 5 = 12 + 5$, so $x = 17.$ To solve $ 10 = n 4$, add 4 to both sides: $ 10 + 4 = n 4 + 4$, so $ 6 = n.$.

Explanation Imagine a balanced scale. If you add a 5 pound weight to the left side, you must also add a 5 pound weight to the right to keep it from tipping over! This is how we isolate the variable in equations involving subtraction. We add the same number back to both sides to 'undo' the subtraction and find our answer.